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2010-05-25T14:21:06Z

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==Create valarray of bool value by using comparison operator on another valarray==

<source lang="cpp">

#include <iostream>
#include <valarray>
#include <cmath>
using namespace std;
int main()
{
valarray<int> v(10);
for(int i=0; i<10; i++)
v[i] = i;
cout << "Original contents: ";
for(int i=0; i<10; i++)
cout << v[i] << " ";
valarray<bool> vb = v < 5;
cout << "Those elements less than 5: ";
for(int i=0; i<10; i++)
cout << vb[i] << " ";
cout << endl;
}
/*
Original contents: 0 1 2 3 4 5 6 7 8 9 Those elements less than 5: 1 1 1 1 1 0 0 0 0 0
*/
</source>

==Do sqrt for all elements in a valarray==

<source lang="cpp">

#include <iostream>
#include <valarray>
#include <cmath>
using namespace std;
int main()
{
valarray<int> v(10);
for(int i=0; i<10; i++)
v[i] = i*i;
cout << "Original contents: ";
for(int i=0; i<10; i++)
cout << v[i] << " \n\n";
v = sqrt(v);
for(int i=0; i<10; i++)
cout << v[i] << " \n\n";

cout << endl;
}
/*
Original contents: 0
1
4
9
16
25
36
49
64
81
0
1
2
3
4
5
6
7
8
9

*/
</source>

==Minus 10 from each element in a valarray==

<source lang="cpp">

#include <iostream>
#include <valarray>
#include <cmath>
using namespace std;
int main()
{
valarray<int> v(10);
for(int i=0; i<10; i++)
v[i] = i;
cout << "Original contents: ";
for(int i=0; i<10; i++)
cout << v[i] << " \n\n";
v = v - 10;
for(int i=0; i<10; i++)
cout << v[i] << " \n\n";

cout << endl;
}
/*
Original contents: 0
1
2
3
4
5
6
7
8
9
-10
-9
-8
-7
-6
-5
-4
-3
-2
-1

*/
</source>

==Print three-dimensional valarray line-by-line==

<source lang="cpp">

/* The following code example is taken from the book
* "The C++ Standard Library - A Tutorial and Reference"
* by Nicolai M. Josuttis, Addison-Wesley, 1999
*
* (C) Copyright Nicolai M. Josuttis 1999.
* Permission to copy, use, modify, sell and distribute this software
* is granted provided this copyright notice appears in all copies.
* This software is provided "as is" without express or implied
* warranty, and with no claim as to its suitability for any purpose.
*/
#include <iostream>
#include <valarray>
using namespace std;
// print three-dimensional valarray line-by-line
template<class T>
void printValarray3D (const valarray<T>& va, int dim1, int dim2)
{
for (int i=0; i<va.size()/(dim1*dim2); ++i) {
for (int j=0; j<dim2; ++j) {
for (int k=0; k<dim1; ++k) {
cout << va[i*dim1*dim2+j*dim1+k] << " ";
}
cout << "\n";
}
cout << "\n";
}
cout << endl;
}
int main()
{
/* valarray with 24 elements
* - two groups
* - four rows
* - three columns
*/
valarray<double> va(24);
// fill valarray with values
for (int i=0; i<24; i++) {
va[i] = i;
}
// print valarray
printValarray3D (va, 3, 4);
// we need two two-dimensional subsets of three times 3 values
// in two 12-element arrays
size_t lengthvalues[] = { 2, 3 };
size_t stridevalues[] = { 12, 3 };
valarray<size_t> length(lengthvalues,2);
valarray<size_t> stride(stridevalues,2);
// assign the second column of the first three rows
// to the first column of the first three rows
va[gslice(0,length,stride)]
= valarray<double>(va[gslice(1,length,stride)]);
// add and assign the third of the first three rows
// to the first of the first three rows
va[gslice(0,length,stride)]
+= valarray<double>(va[gslice(2,length,stride)]);

// print valarray
printValarray3D (va, 3, 4);
}
/*
0 1 2
3 4 5
6 7 8
9 10 11
12 13 14
15 16 17
18 19 20
21 22 23

3 1 2
9 4 5
15 7 8
9 10 11
27 13 14
33 16 17
39 19 20
21 22 23

*/
</source>

==Print valarray as two-dimensional array==

<source lang="cpp">

/* The following code example is taken from the book
* "The C++ Standard Library - A Tutorial and Reference"
* by Nicolai M. Josuttis, Addison-Wesley, 1999
*
* (C) Copyright Nicolai M. Josuttis 1999.
* Permission to copy, use, modify, sell and distribute this software
* is granted provided this copyright notice appears in all copies.
* This software is provided "as is" without express or implied
* warranty, and with no claim as to its suitability for any purpose.
*/
#include <iostream>
#include <valarray>
using namespace std;
// print valarray as two-dimensional array
template<class T>
void printValarray (const valarray<T>& va, int num)
{
for (int i=0; i<va.size()/num; i++) {
for (int j=0; j<num; j++) {
cout << va[i*num+j] << " ";
}
cout << endl;
}
cout << endl;
}
int main()
{
// create valarray for 12 elements
valarray<double> va(12);
// initialize valarray by values 1.01, 2.02, ... 12.12
for (int i=0; i<12; i++) {
va[i] = (i+1) * 1.01;
}
printValarray(va,4);
/* create array of indexes
* - note: element type has to be size_t
*/
valarray<size_t> idx(4);
idx[0] = 8;
idx[1] = 0;
idx[2] = 3;
idx[3] = 7;
// use array of indexes to print the ninth, first, fourth, and eighth elements
printValarray(valarray<double>(va[idx]), 4);
// change the first and fourth elements and print them again indirectly
va[0] = 11.11;
va[3] = 44.44;
printValarray(valarray<double>(va[idx]), 4);
// now select the second, third, sixth, and ninth elements
// and assign 99 to them
idx[0] = 1;
idx[1] = 2;
idx[2] = 5;
idx[3] = 8;
va[idx] = 99;
// print the whole valarray again
printValarray (va, 4);
}
/*
1.01 2.02 3.03 4.04
5.05 6.06 7.07 8.08
9.09 10.1 11.11 12.12
9.09 1.01 4.04 8.08
9.09 11.11 44.44 8.08
11.11 99 99 44.44
5.05 99 7.07 8.08
99 10.1 11.11 12.12

*/
</source>

==Use valarray + valarray to double the value for each element in valarray==

<source lang="cpp">

#include <iostream>
#include <valarray>
#include <cmath>
using namespace std;
int main()
{
valarray<int> v(10);
for(int i=0; i<10; i++)
v[i] = i;
cout << "Original contents: ";
for(int i=0; i<10; i++)
cout << v[i] << " \n\n";
v = v + v;
for(int i=0; i<10; i++)
cout << v[i] << " \n\n";

cout << endl;
}
/*
Original contents: 0
1
2
3
4
5
6
7
8
9
0
2
4
6
8
10
12
14
16
18

*/
</source>

==valarray with double value inside==

<source lang="cpp">

/* The following code example is taken from the book
* "The C++ Standard Library - A Tutorial and Reference"
* by Nicolai M. Josuttis, Addison-Wesley, 1999
*
* (C) Copyright Nicolai M. Josuttis 1999.
* Permission to copy, use, modify, sell and distribute this software
* is granted provided this copyright notice appears in all copies.
* This software is provided "as is" without express or implied
* warranty, and with no claim as to its suitability for any purpose.
*/
#include <iostream>
#include <valarray>
using namespace std;
// print valarray line-by-line
template<class T>
void printValarray (const valarray<T>& va, int num)
{
for (int i=0; i<va.size()/num; ++i) {
for (int j=0; j<num; ++j) {
cout << va[i*num+j] << " ";
}
cout << endl;
}
cout << endl;
}
int main()
{
/* valarray with 12 elements
* - four rows
* - three columns
*/
valarray<double> va(12);
// fill valarray with values
for (int i=0; i<12; i++) {
va[i] = i;
}
printValarray (va, 3);
// assign 77 to all values that are less than 5
va[va<5.0] = 77.0;
// add 100 to all values that are greater than 5 and less than 9
va[va>5.0 && va<9.0] = valarray<double>(va[va>5.0 && va<9.0]) + 100.0;
printValarray (va, 3);
}
/*
0 1 2
3 4 5
6 7 8
9 10 11
77 77 77
77 77 5
106 107 108
9 10 11

*/
</source>

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в 14:21, 25 мая 2010

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